Photocatalytic C-N coupling towards urea synthesis with a palladium-supported CeO2 catalyst

The conversion of N-2 and CO2 into urea through a photocatalytic C-N coupling reaction under ambient conditions serves as a novel green avenue for urea synthesis. However, the poor adsorption and C-N coupling capability of inert gas molecules hinder the efficient catalytic activity. Herein, palladium-decorated CeO2 (Pd-CeO2) was demonstrated as an efficient photocatalyst for C-N coupling reaction and delivered a remarkable urea yield rate of 9.2 mu mol h(-1) g(-1), which was superior to that of pristine CeO2 (2.5 mu mol h(-1) g(-1)). Comprehensive investigations further endorsed that the emerged space-charge region in the CeO2(111)/Pd(111) interface not only effectively facilitates the targeted capture and activation of inert CO2 and N-2 but also stabilizes the formation of key intermediates (*NCON). Besides, the effective inhibition of the endothermic *NNH intermediate is conducive to the subsequent C-N coupling process and the improvement of reaction selectivity. The reaction mechanism was studied in detail by density functional theory (DFT) with the formation of a C-N bond via a thermodynamically spontaneous reaction between *N = N* and CO. This work provides novel insights into the conversion of CO2 and N-2 into urea.

Automated summary

The conversion of N-2 and CO2 into urea through a photocatalytic C-N coupling reaction under ambient conditions is a novel green synthesis approach. Palladium-decorated CeO2 (Pd-CeO2) has been demonstrated to be an efficient photocatalyst for this reaction, yielding a high rate of urea production. The interface between Pd and CeO2 facilitates the capture and activation of CO2 and N-2, while also stabilizing the formation of key intermediates (*NCON). The inhibition of the endothermic *NNH intermediate improves the reaction selectivity and promotes the C-N coupling process.